Lactic acid bacteria (LAB) are Gram-positive commensals of the mammalian gastrointestinal tract that have also been used in food preservation for millennia. In more recent industrialised eras, co-incident with the development of Microbiology as a scientific discipline, they have been used more systematically, and now form the foundation of worldwide dairy and food fermentation industries (cheese, yoghurts, fermented hams and sausages, condiments such as fish and soy sauces). In the last few decades LAB have been ingested directly for human and animal health purposes in the form of probiotic yoghurts, beverages and other supplements. Although environmentally ubiquitous, LAB are nutritionally fastidious bacteria, whose culture is complex, involving specialised microaerophilic atmospheres and specific, multi-component culture media. Thus any new innovation which can simplify either cultivation parameter without requiring significant changes in existing fermenter technology is likely to find wide scale application.
Although very important in the dairy, fermented food and more recently health care associated industries, LAB are regarded as unwelcome contaminants in the brewing and wine production industries. Lactic acid bacteria possess a remarkable ability to survive in liquid media that are acidic, cold and anaerobic. These are the typical physical characteristics of beer, lagers and wine, and are environmental conditions that most other microbes find very hostile. In addition to their tolerance of such conditions, lactic acid bacteria also have the tendency to ferment any residual sugars they encounter in beer or wine to lactic acid, which, along with other LAB metabolites, can impart undesirable sour and similar ‘off’ tastes. Thus, there is a considerable global market in media for LAB diagnostics in the beverage fermentation industries. LAB isolates from beer and wine are generally difficult to culture, as they have undergone considerable environmental stresses during the various fermentation procedures they will have experienced and are often slow to revert to active growth. It can take up to a week to culture beer LAB contaminants on the optimal culture media for LAB, MRS medium, and indeed some LAB contaminants can take even longer than this to be restored, which can have disastrous consequences for the fate of the contaminated beverage during its subsequent long storage/maturation process.
The identification of factors which can enhance or promote growth of LAB is therefore of considerable commercial significance.
Bananas (Musa spp) are known to have a number of properties which can affect the growth of bacteria. It has been reported (Lyte, 1997, FEMS Microbiology Letters 154:245-250) that extract from bananas can promote the growth of Gram negative bacteria such as E. coli. The effects of the banana extract growth induction were found to be due to the presence of neurochemicals such as noradrenaline (norepinephrine) and dopamine in the banana extract.
U.S. Pat. No. 5,629,349 describes the initial use of neurochemicals in growth enhancement of bacteria, and cites references foodstuffs such as bananas and plantains as sources of dietary noradrenaline and dopamine. However, the 1997 Lyte publication stated that no effect of either the banana extract or neurochemical supplements could be seen on the growth of Gram positive bacteria.
International Patent Application WO2004/069143 describes the medicinal use of banana or plantain extract for treatment of inflammatory bowel disease; the publication suggests that banana extract will prevent or inhibit bacterial growth, and may prevent bacterial adhesion to the intestinal wall.
The present inventors have surprisingly found that, contrary to the reported suppressive effects on Gram positive bacterial growth of bananas, a banana extract can actually promote growth of Gram positive bacteria, and of LAB in particular. We have also determined that the extract effectively promotes growth of environmentally stressed bacteria. We further believe that the extract may be used to improve the viability of a bacterial sample.
It is also believed that extracts having the same or similar properties may be obtained from other plants; in particular apple, orange, plum, carrot, tea, and coffee.